This invention relates to electric storage batteries in general and more particularly to lead-acid batteries for use in motive power applications such as mining equipment, forklift trucks, and the like.
Batteries used in motive power applications are very often subjected to abuse. This is particularly true when these batteries are used to power mining equipment. Mines provide a very harsh atmosphere for equipment that is used therein. The mine atmosphere contains an abundance of dirt, rock dust, coal particles, as well as moisture and acid due to seepage. In addition, there is always the potential of a build up of explosive gases. As extreme as this environment is for the usual operating equipment, it poses very formidable problems for batteries.
When using batteries, there is always the potential for short circuits to develop which could result in the generation of sparks, flames or other hot spots which in turn could ignite in the explosive atmosphere. In a mining atmosphere, the probability of this occurring is greatly increased due to the creation of leakage paths caused by accummulations of the dirt, rock dust, coal particles, moisture and acid as well as mechanical abuses caused by physical contact with the rib timbers, lifting mechanism, cleaning tools and/or the machine itself in which the battery is used. In addition, the battery itself can contribute to the creation of a hazardous explosive atmosphere as a result of generation of hydrogen gas.
Some attempts have been made in the past to obviate the problems discussed above. For example, in order to permit the dissipation of hydrogen gas and corrosive acidic vapors, the battery tray or box incorporated a louver along one side edge thereof which proported to serve three functions: the first being to prevent the accummulation of hazardous gases within the battery box from forming by allowing these gases to be vented to the surrounding atmosphere; secondly, forming a physical barrier to prevent foreign objects, such as tools and other metallic or electrically conducted objects from entering the tray and shorting out and/or damages the cells therein; and thirdly, since at least one portion of the bottom of the louver was at substantially the same level as the top of an adjacent cell, a drain was provided for run off of water and other debris lodge cleaning.
One prior art louver was formed by creating a pair of recesses along the top edge of one side of a battery tray then bolting a flanged member across the recesses whereby a pair of elongated vents would be formed therebetween. One of the problems associated with this feature was that the flange member, by necessity, extended beyond the exterior surface of the battery tray and subsequently was prone to denting and other physical abuse which could not only deform the flange itself, it could also deform the tray which in turn could possibly cause injury to the cells therein, causing short circuits, due to rupture of the cell jar, leakage of the acid and other undesirable effects.
The prior art design for containor vents included closed corners and sides which were thought to be beneficial in that they would shield the output terminals from outside penetration. The prior art design took advantage of the situation by placing the output terminals in the closed corners for protection. This layout was also thought to have an additional beneficial effect in that it minimized the voltage between cells. This created a serious drawback however in that these closed corners and sides have the exceptional ability to collect, and successfully hold the dirt, rock dust, coal particles, moisture and acid. The result of this mixture is a conducting film covering the tray insulating material and touching the terminals. The effect of this is essentially the same as if the terminals were actually touching the tray insulation.
Additional problems were created in that, in prior art designs, the insulating material had a tendency to develop conducting paths and to peel away from the metallic tray thereby exposing the metal to the conducting film. These failures appear to be largely due to small pin holes developing in the insulating material. If there is even a minute hole, the voltage pressure, combined with the superior penetrating properties of the acid, will provide an electrical connection from the terminals to the tray. In addition, the penetrating acid tends to cause the insulating material to peel away.
As previously stated, this insulation failure is also traceable to physical contact with the rib timbers, battery cover, lifting mechanism, cleaning tools, or the machine itself. However, the greatest proportion of problems caused can be directly attributable to the magnitude of the voltage differences and conducting resistance of the leakage path. Low levels of voltage do not have the pressure necessary to supply enough current to cause problems. However, at about forty volts, the leakage becomes noticeable. The maximum voltage generally exists just before the end of the charge cycle. At this point in time, the current through all the leakage paths is the highest and the ability to generate sparks is the greatest. In addition, the hydrogen generated by the battery during charging is also produced at its maximum volume.